Triton (moon) | Space Wiki | Fandom powered by Wikia Discovery and naming William Lassell, the discoverer of Triton The moon was discovered by British astronomer William Lassell on October 10, 1846, [6] just 17 days after Neptune was discovered by German astronomers Johann Gottfried Galle and Heinrich Louis d'Arrest , who were following coordinates given to them by French astronomer and mathematician Urbain Le Verrier . A brewer by trade, Lassell began making mirrors for his amateur telescope in 1820. When John Herschel received news of Neptune's discovery, he wrote to Lassell suggesting he search for possible moons. Lassell did so and discovered Triton eight days later. [7] [6] Lassell also claimed to have discovered rings. Although Neptune was later confirmed to have rings, they are so faint and dark that it is doubted he actually saw them. [8] Triton is named after the Greek sea god Triton (Τρίτων), the son of Poseidon (the Greek god comparable to the Roman Neptune ).

The name was first proposed by Camille Flammarion in his 1880 book Astronomie Populaire, [9] although it was not officially adopted until many decades later. [10] Until the discovery of the second moon Nereid in 1949, Triton was commonly known as simply "the satellite of Neptune". Lassell did not name his own discovery, although he suggested names a few years after his subsequent discovery of an eighth moon of Saturn ( Hyperion ). The third and fourth moons of Uranus ( Ariel and Umbriel ), which Lassell discovered in 1851, were named by John Herschel . [11] Orbit and rotation Triton is unique among all large moons in the Solar System for its retrograde orbit around its planet (i.e., it orbits in a direction opposite to the planet's rotation). Most of the outer irregular moons of Jupiter and Saturn also have retrograde orbits, as do some of Uranus 's outer moons.

However, these moons are all much more distant from their primaries, and are quite small in comparison; the largest of them ( Phoebe ) [lower-alpha 1] has only 8% of the diameter (and 0.03% of the mass) of Triton. Triton's orbit is associated with two tilts, the inclination of Neptune's spin to Neptune's orbit, 30°, and the inclination of Triton's orbit to Neptune's spin, 157° (an inclination over 90° indicates retrograde motion). Triton's orbit precesses forward relative to Neptune's spin with a period of about 678 Earth years (4.1 Neptunian years), [12] [13] making its Neptune-orbit-relative inclination vary between 127° and 173°. That inclination is currently 130°; Triton's orbit is now near its maximum departure from coplanarity with Neptune's. Triton is in synchronous rotation with Neptune; it keeps one face oriented toward the planet at all times. Its equator is almost exactly aligned with its orbital plane.

[14] At the present time, Triton's rotational axis is about 40° from Neptune's orbital plane, and hence at some point during Neptune's year each pole points fairly close to the Sun, almost like the poles of Uranus. As Neptune orbits the Sun, Triton's polar regions take turns facing the Sun, resulting in seasonal changes as one pole, then the other, moves into the sunlight. Such changes have recently been observed. [15] Triton's revolution around Neptune has become a nearly perfect circle with an eccentricity of almost zero. Viscoelastic damping from tides alone is not thought to be capable of circularizing Triton's orbit in the time since the origin of the system, and gas drag from a prograde debris disc is likely to have played a substantial role. [12] [13] Tidal interactions also cause Triton's orbit, already closer to Neptune than the Moon's to Earth, to slowly decay further; predictions are that some 3.6 billion years from now, Triton will pass within Neptune's Roche limit .

[16] This will result in either a collision with Neptune's atmosphere or the breakup of Triton, forming a ring system similar to that found around Saturn . [16] Capture The Kuiper belt (green), in the Solar System's outskirts, is where Triton is thought to have originated. Because moons in retrograde orbits cannot have formed out of the same region of the solar nebula as the planets they orbit, it must have been captured from elsewhere. It is suspected that Triton was captured from the Kuiper belt , [1] a ring of small icy objects extending outward from just inside the orbit of Neptune to about 50 AU from the Sun. Thought to be the point of origin for the majority of short-period comets observed from Earth, it is also home to several large, planet-like bodies including Pluto , which is now recognized as the largest in a population of Kuiper belt objects (the plutinos ) locked in orbital step with Neptune. Triton is only slightly larger than Pluto and nearly identical in composition, which has led to the hypothesis that the two share a common origin.

[17] The proposed capture of Triton may explain several features of the Neptunian system, including the extremely eccentric orbit of Neptune's moon Nereid and the scarcity of moons as compared to the other gas giants. Triton's initially eccentric orbit would have intersected orbits of irregular moons and disrupted those of smaller regular moons, dispersing them through gravitational interactions. [12] [13] Triton's eccentric post-capture orbit would have also resulted in tidal heating of the moon's interior. This would have kept Triton liquid for a billion years, which is supported by evidence of differentiation in the moon's interior. [5] This source of internal heat disappeared following circularization of the orbit. Two types of mechanisms have been proposed for Triton's capture. In order to be gravitationally captured by a planet, a passing body must lose sufficient energy to be slowed down to a speed less than that required to escape. An early theory of how Triton may have been slowed was by collision with another object, either one that happened to be passing by Neptune (which is unlikely), or a moon or proto-moon in orbit around Neptune (which is more likely).

[3] A more recent and now favored hypothesis suggests that, before its capture, Triton had a massive companion similar to Pluto's moon Charon with which it formed a binary. When the binary encountered Neptune, it interacted in such a way that orbital energy was transferred from Triton to its companion; the latter was expelled, while Triton became bound to Neptune. This hypothesis is supported by several lines of evidence, including binaries being very common among the large Kuiper belt objects. [18] [19] The event was brief but gentle, saving Triton from collisional disruption. Events like this may have been common during the formation of Neptune, or later when it migrated outward . [1] Physical characteristics Triton's mass (blue), shown as a fraction of the total, dominates the Neptunian moon system, with all other moons combined comprising only one third of one percent. This imbalance may reflect the elimination of many of Neptune's original satellites following Triton's capture. Triton (lower left) compared to the Moon (upper left) and Earth (right), to scale.

Triton is the seventh largest moon and sixteenth largest object in the Solar System, and is modestly larger than the dwarf planets Pluto and Eris . It comprises more than 99.5% of all the mass known to orbit Neptune, including the planet's rings and twelve other known moons, [lower-alpha 2] and is also more massive than all known moons in the Solar System smaller than itself combined. [lower-alpha 3] It has a radius, density (69), temperature and chemical composition similar to those of Pluto . [20] As with Pluto, 55% of Triton's surface is covered with frozen nitrogen, with water ice comprising 15–35% and dry ice (frozen carbon dioxide ) forming the remaining 10–20%. Trace ices include 0.1% methane and 0.05% carbon monoxide . [3] There could also be ammonia on the surface if ammonia dihydrate is present as suspected in the lithosphere . [21] Triton's density implies it is probably about 30–45% water ice , with the remainder being rocky material.

[3] Triton's surface area is 23 million km2, which is 4.5% of Earth , or 15.5% of Earth's land area. Triton has a considerably high albedo , reflecting 60–95% of the sunlight that reaches it. By comparison, Earth's moon reflects only 11%. [22] Triton's reddish colour is thought to be the result of methane ice, which is converted to tholins under bombardment from ultraviolet radiation. [3] [23] Because Triton's surface indicates a long history of melting, models of its interior posit that Triton is differentiated, like Earth , into a solid core , a mantle and a crust . Water , the most abundant volatile in the Solar System, comprises the moon's mantle, which lies over a core of rock and metal. There is enough rock in Triton's interior for radioactive decay to power convection in the mantle. The heat may even be sufficient to maintain a "subterranean ocean" similar to that which is hypothesized to exist underneath the surface of Europa .

[3] [24] If present, a layer of liquid water would suggest the possibility, however unlikely, of life. [25] Artist's impression of Triton, showing its tenuous atmosphere just over the limb. Triton has a tenuous nitrogen atmosphere, with trace amounts of carbon monoxide and small amounts of methane near the surface. [26] [27] [28] Like Pluto's atmosphere, the atmosphere of Triton is thought to have resulted from evaporation of nitrogen from its surface. [17] The surface temperature is at least Template:Val ( Template:Val ) because Triton's nitrogen ice is in the warmer, hexagonal crystalline state, and the phase transition between hexagonal and cubic nitrogen ice occurs at that temperature. [29] An upper limit in the low 40s (K) can be set from vapor pressure equilibrium with nitrogen gas in Triton's atmosphere. [30] This temperature range is colder than Pluto 's average equilibrium temperature of Template:Val ( Template:Val ). Triton's surface atmospheric pressure is only about 1.4– Template:Val (0.014– Template:Val ).

[3] Clouds observed above Triton's limb by Voyager 2 Turbulence at Triton's surface creates a troposphere (a "weather region") rising to an altitude of 8 km. Streaks on Triton's surface left by geyser plumes suggest that the troposphere is driven by seasonal winds capable of moving material of over a micrometre in size. [31] Unlike other atmospheres, Triton's lacks a stratosphere , and instead has a thermosphere from altitudes of 8 to 950 km, and an exosphere above that. [3] The temperature of Triton's upper atmosphere, at Template:Val , is higher than that at the surface, due to heat absorbed from solar radiation and Neptune's magnetosphere . [26] [32] A haze permeates most of Triton's troposphere, thought to be composed largely of hydrocarbons and nitriles created by the action of sunlight on methane. Triton's atmosphere also possesses clouds of condensed nitrogen that lie between 1 and 3 km from the surface.

[3] In the 1990s, observations from Earth were made of Triton's limb as the moon passed in front of stars . These observations indicated the presence of a denser atmosphere than was deduced from Voyager 2 data. [33] Other observations have shown an increase in temperature by 5% from 1989 to 1998. [34] These observations indicate Triton is approaching an unusually warm summer season that only happens once every few hundred years. Theories for this warming include a change of frost patterns on Triton's surface and a change in ice albedo , which would allow more heat to be absorbed. [35] Another theory argues the changes in temperature are a result of deposition of dark, red material from geological processes on the moon. Because Triton's Bond albedo is among the highest within the Solar System , it is sensitive to small variations in spectral albedo. [36] Surface features All detailed knowledge of the surface of Triton was acquired in a single encounter by the Voyager 2 spacecraft in 1989.

The 40% of Triton's surface imaged by Voyager revealed blocky outcrops, ridges, troughs, furrows, hollows, plateaus, icy plains and few craters. Triton is relatively flat; its observed topography never varies beyond a kilometer. [3] There are relatively few impact craters on Triton. Recent analysis of crater density and distribution has suggested that in geological terms, Triton's surface is extremely young, with regions varying from 50 million years old to just 6 million years old. [37] Cryovolcanism Main article: Cryovolcano Dark streaks across Triton's south polar cap surface, thought to be dust deposits left by eruptions of nitrogen geysers Triton is geologically active; its surface is young and has relatively few impact craters. Although Triton is made of various ices, its subsurface processes are similar to those that produce volcanoes and rift valleys on Earth, but with water and ammonia lavas as opposed to liquid rock. [3] Triton's entire surface is cut by complex valleys and ridges, probably the result of tectonics and icy volcanism .

The vast majority of surface features on Triton are endogenic —the result of internal geological processes rather than external processes such as impacts. Most are volcanic and extrusive in nature, rather than tectonic . [3] The Voyager 2 probe observed a handful of geyser -like eruptions of invisible nitrogen gas and entrained dust from beneath the surface of Triton in plumes up to 8 km high. [20] [38] Triton thus joins the Earth , Io , and Enceladus as one of the few worlds of the Solar System on which active eruptions of some sort have been observed. [39] ( Venus , Mars , Europa , Titan , and Dione may also be volcanically active.) The best observed examples were named Hili and Mahilani (after a Zulu water sprite and a Tongan sea spirit, respectively). [40] All the geysers observed were located between 50° and 57°S, the part of Triton's surface close to the subsolar point . This indicates that solar heating, although very weak at Triton's great distance from the Sun, plays a crucial role.

It is thought that the surface of Triton probably consists of a translucent layer of frozen nitrogen overlying a darker substrate, which creates a kind of "solid greenhouse effect ". Solar radiation passes through the surface ice, slowly heating and vaporizing subsurface nitrogen until enough gas pressure accumulates for it to erupt through the crust. [3] [31] A temperature increase of just 4 K above the ambient surface temperature of 37 K could drive eruptions to the heights observed. [38] Although commonly termed "cryovolcanic", this nitrogen plume activity is distinct from Triton's larger scale cryovolcanic eruptions, as well as volcanic processes on other worlds, which are powered by the internal heat of the body in question. Analogous plumes of gaseous CO2 are thought to erupt from the south polar cap of Mars each spring. [41] Each eruption of a Triton geyser may last up to a year, driven by the sublimation of about 69 of nitrogen ice over this interval; dust entrained may be deposited up to 150 km downwind in visible streaks, and perhaps much farther in more diffuse deposits.

[38] Voyager's images of Triton's southern hemisphere show many such streaks of dark material. [42] Between 1977 and the Voyager flyby in 1989, Triton shifted from a reddish colour, similar to Pluto, to a far paler hue, suggesting that in the intervening decade lighter nitrogen frosts had covered older reddish material. [3] The eruption of volatiles from Triton's equator and their deposition at the poles may redistribute enough mass over the course of 10,000 years to cause polar wander . [43] Polar cap, plains and ridges Triton's bright south polar cap above a region of cantaloupe terrain The southern polar region of Triton is covered by a highly reflective cap of frozen nitrogen and methane sprinkled by impact craters and openings of geysers. Little is known about the north pole because it was on the night side during the Voyager 2 encounter. However, it is thought that Triton must also have a north polar cap.

[29] The high plains found on Triton's eastern hemisphere, such as Cipango Planum, cover over and blot out older features, and are therefore almost certainly the result of icy lava washing over the previous landscape. The plains are dotted with pits, such as Leviathan Patera , which are probably the vents from which this lava emerged. The composition of the lava is unknown, although a mixture of ammonia and water is suspected. [3] Four roughly circular "walled plains" have been identified on Triton. They are the flattest regions so far discovered, with a variance in altitude of less than 200 m . They are thought to have formed from eruption of icy lava. [3] The plains near Triton's eastern limb are dotted with black spots, the maculae . Each of the maculae comprises a dark central patch surrounded by a white halo of material. They all have similar diameters of between 20 and 30 km. Some speculate the maculae are outliers of the southern polar cap, which is in retreat in summer. [3] There are extensive ridges and valleys in complex patterns across Triton's surface, probably the result of freeze–thaw cycles.

[44] Many also appear to be tectonic in nature and may result from extension or strike-slip faulting . [45] There are long double ridges of ice with central troughs bearing a strong resemblance to Europan lineae (although they have a larger scale [2] ), and which may have a similar origin, [3] possibly shear heating from strike-slip motion along faults caused by diurnal tidal stresses experienced before Triton's orbit was fully circularized. [2] These faults with parallel ridges expelled from the interior cross complex terrain with valleys in the equatorial region. The ridges and furrows, or sulci , such as Yasu Sulci , Ho Sulci , and Lo Sulci , [46] are thought to be of intermediate age in Triton's geological history, and in many cases to have formed concurrently. They tend to be clustered in groups or "packets". [45] Cantaloupe terrain Cantaloupe terrain viewed from 130,000 km by Voyager 2 , with crosscutting Europa -like double ridges. Slidr Sulci (vertical) and Tano Sulci form the prominent "X".

Triton's western hemisphere consists of a strange series of fissures and depressions known as "cantaloupe terrain" because of its resemblance to the skin of a cantaloupe melon. Although it has few craters, it is thought that this is the oldest terrain on Triton. [47] It probably covers much of the western half of the moon. [3] Cantaloupe terrain, which is mostly dirty water ice, is known to exist only on Triton. It contains depressions 30–40 km in diameter. [47] The depressions (cavi) are probably not impact craters because they are all of similar size and have smooth curves. The leading hypothesis for their formation is diapirism , the rising of "lumps" of less dense material through a stratum of denser material. [3] [48] Alternate hypotheses include formation by collapses, or by flooding caused by cryovolcanism . [47] Impact craters Tuonela Planitia (left) and Ruach Planitia (center) are two of Triton's cryovolcanic "walled plains".

The paucity of craters is evidence of extensive geologic activity. Due to constant erasure and modification by ongoing geological activity, impact craters on Triton's surface are relatively rare. A census of Triton's craters imaged by Voyager 2 found only 179 that were incontestably of impact origin, compared with 835 observed for Uranus' moon Miranda , which has only three percent of Triton's surface area . [49] The largest crater observed on Triton thought to have been created by an impact is a 27 km-diameter feature called Mazomba . [49] [50] Although larger craters have been observed, they are generally thought to be volcanic in nature. [49] The few impact craters on Triton are almost all concentrated in the leading hemisphere—that facing the direction of the orbital motion—with the majority concentrated around the equator between 30° and 70° longitude, [49] resulting from material swept up from orbit around Neptune.

[37] Because it orbits with one side permanently facing the planet, astronomers expect that Triton should have fewer impacts on its trailing hemisphere, as impacts on the leading hemisphere would be more frequent and more violent. [49] However, as Voyager only imaged 40% of Triton's surface, this remains uncertain. Observation and exploration Neptune (top) and Triton (bottom) three days after Voyager 2's flyby The orbital properties of Triton had been defined with high accuracy in the 19th century. It was found to have a retrograde orbit, at a very high angle of inclination to the plane of Neptune's orbit. The first detailed observations of Triton were not made until 1930. Little was known about the satellite until Voyager 2 arrived at the end of the 20th century. [3] Before the arrival of Voyager 2, astronomers suspected that Triton might have liquid nitrogen seas and a nitrogen/methane atmosphere with a density as much as 30% that of the Earth. Like the famous overestimates of the atmospheric density of Mars, this was completely false. As with Mars, a denser atmosphere is postulated for the body's early history.

[51] The first attempt to measure the diameter of Triton was made by Gerard Kuiper in 1954. He obtained a value of 3,800 km. Subsequent measurement attempts arrived at values ranging from 2,500 to 6,000 km, or from slightly smaller than our Moon to nearly half the diameter of Earth. [52] Data from the approach of Voyager 2 to Neptune on August 25, 1989, led to a more accurate estimate of Triton's diameter (2,706 km). [53] In the 1990s, various observations from Earth were made of the limb of Triton using the occultation of nearby stars, which indicated the presence of an atmosphere and an exotic surface. The observations suggest that the atmosphere is denser than the Voyager 2 measurements had indicated. [33] New concepts for missions to the Neptune system to be conducted in the 2010s have been brought forward by NASA scientists on numerous occasions over the last decades.

All of them identified Triton as being a prime target and a separate Triton lander comparable to the Huygens probe for Titan was frequently included in those plans. To date, however, no efforts aimed at Neptune and Triton went beyond the proposal phase and NASA's funding on missions to the outer solar system is currently focused on the Jupiter and Saturn systems. [54] See also ^ a b c Prockter, L. M.; Nimmo, F.; Pappalardo, R. T. (2005-07-30). "A shear heating origin for ridges on Triton" . Geophysical Research Letters 32 (14): L14202. Bibcode 2005GeoRL..3214202P . doi : 10.1029/2005GL022832 . Retrieved 2011-10-09. ^ a b William Lassell (November 12, 1847). "Lassell's Satellite of Neptune". Monthly Notices of the Royal Astronomical Society8 (1): 8.

Bibcode 1847MNRAS...8....9B . ^ William Lassell (November 13, 1846). "Discovery of Supposed Ring and Satellite of Neptune". Monthly Notices of the Royal Astronomical Society 7 (9): 157. Bibcode 1846MNRAS...7..157L . William Lassell (December 11, 1846). "Physical observations on Neptune". Monthly Notices of the Royal Astronomical Society7 (10): 167–168. Bibcode 1847MNRAS...7..297L . Lassell, W. (1847). "Observations of Neptune and his satellite".Monthly Notices of the Royal Astronomical Society 7 (17): 307–308. Bibcode 1847MNRAS...7..307L . doi : 10.1002/asna.18530360703 . ^ Smith, R. W.; Baum, R. (1984).

"William Lassell and the Ring of Neptune: A Case Study in Instrumental Failure". Journal of the History of Astronomy 15 (42): 1–17. Bibcode 1984JHA....15....1S . Triton: Neptune's Odd Moon Triton: Neptune's Odd Moon By Elizabeth Howell, Space.com Contributor | June 30, 2016 06:12pm ET MORE The crescent planet Neptune and its crescent moon Triton, as seen by NASA's Voyager 2 spacecraft in 1989. Credit: Voyager 2, NASA Triton is the largest of Neptune's moons. Discovered in 1846 by British astronomer William Lassell – just weeks after Neptune itself was found – the moon showed some strange characteristics as astronomers learned more about it. To NASA's knowledge, Triton is the only moon in the solar system that orbits in a direction opposite to the rotation of its planet . Additionally, its surface is a study of contrasts, with smooth plains appearing to be right next to cratered surfaces.

No spacecraft has gone to Neptune since the 1980s, but telescopes are capturing new data on Triton from the ground. A notable recent find was discovering seasons on the moon , using the European Southern Observatory's Very Large Telescope in Chile. Renewed interest in Triton began shortly after the New Horizons mission flew past Pluto in 2015. NASA released the best high-resolution map of Triton to date in 2014 in anticipation of the flyby, because it is believed that Triton and Pluto could share a similar history. They are of similar size, have nitrogen in their atmospheres and also icy surfaces. Discovery and flyby Triton was found on Oct. 10, 1846, just 17 days after Neptune was discovered. According to NASA, Triton was known simply as " the satellite of Neptune " until 1949, when a second moon (Nereid) was found. All of Neptune's moons, according to International Astronomical Union guidelines, are named after Roman or Greek mythological characters associated with Neptune, Poseidon or oceans. Astronomers had to wait well over a century to see Triton as more than a dot, however.

In 1977, NASA sent two Voyager probes on a one-way trip through the outer solar system, taking advantage of a rare planetary alignment that allowed them to move from one location to the next without using a lot of fuel. Voyager 2 flew by Neptune and its system on Aug. 25, 1989. Among the spacecraft's most stunning finds: icy volcanism is likely taking place on Triton's surface . Voyager 2 took pictures of "several geyser-like volcanic vents that were apparently spewing nitrogen gas laced with extremely fine, dark particles," NASA later wrote on a website. The agency estimates the particles go as high as five miles (eight kilometers) before flowing downwind and striking the surface. It also appears that a large portion of the surface has melted. NASA said that is probably because Neptune captured Triton, causing tidal heating that could have left the satellite liquid for at least one billion years. New discoveries after Voyager 2 Although no spacecraft will go by Neptune's system in the near future, computer models and higher-resolution telescopes on Earth are providing new information about Triton's history and environment.

(NASA has also released new pictures of Triton from Voyager 2 at least as late as 2009.) In 2006, a model published in Nature suggested Triton was originally a binary system that passed too close to Neptune . The planet then pulled Triton away from its companion, which is possible because one member of the system always moves slower than the other. Four years later, long-range infrared observations with the European Southern Observatory's Very Large Telescope revealed that the thin atmosphere of Triton changes with the seasons. At the time the VLT looked at the planet, it was summer in the southern hemisphere, where the sun's warmth thickened the atmosphere . This color photo of Neptune's largest moon Triton was obtained by NASA's Voyager 2 probe on Aug. 24, 1989, from 330,000 miles away. The resolution is about 6.2 miles, sufficient to begin to show topographic detail. Credit: NASA/JPL New models of Neptune could also provide insights on Triton, such as one released in 2015 that looks at the gas giant's magnetosphere.

The magnetic field appears to be particularly pronounced on one side , according to Voyager 2 data and the model, and scientists next want to figure out how this field could interact with Triton. Other information about Triton's history could come from studying small bodies in the solar system, such as Comet 67P/Churyumov–Gerasimenko. The Rosetta spacecraft gathered data that showed molecular nitrogen on the comet's surface in 2015. From that information, scientists are trying to figure out where the nitrogen came from and how it compares to other bodies with nitrogen in the solar system, such as Triton and Pluto. Astrobiologists are also considering that Triton could have water under its icy surface. "I think it is extremely likely that a subsurface ammonia-rich ocean exists in Triton," said the University of Maryland's Saswata Hier-Majumder in a 2012 Astrobiology Magazine article republished on SPACE.com.

“[But] there are a number of uncertainties in our knowledge of Triton's interior and past, which makes it difficult to predict with absolute certainty." One example: because no one is quite sure of the size of Triton's rocky core, that creates difficulty with calculating the amount of heating produced by the decay of radioactive isotopes, also known as radiogenic heating. More heating would increase the size of the ocean. Editor's Recommendations The moon Triton - History, orbit, atmosphere, surface, structure, exploration The moon Triton Triton. © based on NASA images Triton is the largest of Neptune’s moons. Triton has a diameter of roughly 2,700 kilometers. It rotates and orbits Neptune every 5.9 Earth days. And it is the seventh largest moon in solar system. While Neptune has a dozen other moons, Triton’s mass is literally twenty times greater than the rest of the moons put together. Triton is about two thirds the size of Earth’s moon. Triton is unique for being a large moon with a retrograde orbit and its exotic early history.

History of Triton Triton may have originated in the Kuiper Belt, a region beyond Neptune filled with rocky bodies ranging from tiny asteroids to the Plutoids. The Plutoids include the dwarf planet Pluto and similarly sized objects like Sedna and Makemake. This theory is further supported by the melted and reformed surface of Triton, giving it a relatively smooth surface. This theory is also backed up by the fact that Pluto itself crosses Neptune’s orbit; this means that Triton could have been a similar dwarf planet that crossed Neptune’s orbit but was captured by its gravity. Triton was discovered in 1846. William Lassell discovered Triton almost three weeks after Neptune itself was discovered by German astronomers. Triton is named for a son of the Greek god Poseidon or Neptune. Triton's odd orbit Triton is unique for being a large moon with a retrograde orbit. © NASA Triton orbits Neptune every 141 hours. Triton also rotates once per orbit, so that the same side always faces Neptune. Triton is unique because it is the only large moon that has a retrograde orbit, an orbit opposite of the planet’s rotation.

There are many small moons that have retrograde orbits which are known to be captured asteroids, including Neptune’s moon Nereid. However, Triton is the only large moon with this trait. Because of Triton’s eccentric orbit, it is the only moon whose polar regions alternate in facing the sun. However, Triton is not the only large orbit with this habit. Uranus also rotates on its side, presenting rotating such that its North and South poles alternate facing the Sun. Impact of Neptune’s pull on Triton Triton has a faint atmosphere. The thin atmosphere contains traces of methane, but it is mostly nitrogen. Triton has volcanic activity in the form of geysers. Neptune exerts significant tidal forces on Neptune. This has slowed its orbit, pulling Triton closer to Neptune to its current location. Tidal forces also power the volcanic activity on Triton, though it spews nitrogen gases instead of molten rock like Jupiter’s Io. Triton‘s orbit is not stable. The gravitational pull of Neptune on the moon’s orbit will eventually pull Triton into Neptune or cause it to break up. Surface of Triton Kuiper Belt. © NASA images Triton has very few craters but several large cracks.

This may mean that it is geologically very young, that the surface is very young, or that Triton drifted far out in space away from other objects that could impact it. If Triton is a captured dwarf planet, the tidal forces that currently drive its volcanic activity could have melted and reformed the surface, giving it the relatively smooth surface we see today. It has been theorized that the tidal forces of Neptune on the moon could have kept its surface liquid for up to a billion years. Triton could have also impacted one of Neptune’s earlier moons, putting it in an irregular orbit and melting much of the surface. This theory would also account for Neptune‘s faint ring and the four small moons within Neptune’s ring. Triton is one of the coldest objects in the solar system. Its surface temperature has been recorded to be as low as -235°C or 34°° Kelvin. Other temperature measurements have found the temperature to average 38° Kelvin, which is just above absolute zero. Absolute zero is the temperature at which even molecular hydrogen comes to rest and these temperatures were recorded during Neptune’s spring, which reached its summer solstice in 2000.

Triton is so cold that nitrogen becomes a solid, raining down as frost on the night side of the moon. Only Pluto and other Kuiper objects are thought to be as cold. Triton’s surface would appear red to a casual observer. The methane ice on its surface has been converted to compounds called tholins. These red colored molecules are the result of hydrocarbons exposed to ultraviolet light. Inside Triton Triton - In Depth | Planets - NASA Solar System Exploration Planets Triton: In Depth: Triton has a sparsely cratered surface with smooth volcanic plains, mounds and round pits formed by icy lava flows. Triton is the largest of Neptune 's 13 moons. It is unusual because it is the only large moon in our solar system that orbits in the opposite direction of its planet's rotation -- a retrograde orbit. Scientists think Triton is a Kuiper Belt Object captured by Neptune's gravity millions of years ago. It shares many similarities with Pluto , the best known world of the Kuiper Belt. Like our own moon, Triton is locked in synchronous rotation with Neptune -- one side faces the planet at all times.

But because of its unusual orbital inclination both polar regions take turns facing the Sun. Triton has a diameter of 2,700 km (1,680 miles). Spacecraft images show the moon has a sparsely cratered surface with smooth volcanic plains, mounds and round pits formed by icy lava flows. Triton consists of a crust of frozen nitrogen over an icy mantle believed to cover a core of rock and metal. Triton has a density of about 2.050 g per cubic cm (The density of water is 1.0 g per cubic cm.) This is a higher density than that measured for almost any other satellite of an outer planet. (Europa and Io have higher densities.) This implies that Triton contains more rock in its interior than the icy satellites of Saturn and Uranus. Voyager 2 captured this stunning view after it passed Neptune and Triton. Triton's thin atmosphere is composed mainly of nitrogen with small amounts of methane. This atmosphere most likely originates from Triton's volcanic activity, which is driven by seasonal heating by the Sun.

Triton, Io and Venus are the only bodies in the solar system besides Earth that are known to be volcanically active at the present time. Triton is one of the coolest objects in our solar system. It is so cold that most of Triton's nitrogen is condensed as frost, giving its surface an icy sheen that reflects 70 percent of the sunlight that hits it. NASA's Voyager 2 -- the only spacecraft to fly past Neptune and Triton -- found surface temperatures of -235°C (-391°F). During its 1989 flyby, Voyager 2 also found Triton has active geysers, making it one of the few geologically active moons in our solar system. Discovery: Triton was discovered on 10 October 1846 by British astronomer William Lassell, just 17 days after Neptune itself was discovered by German astronomers Johann Gottfried Galle and Heinrich Louis d'Arrest. How Triton Got its Name: Moons of Neptune are named for characters from Greek or Roman mythology associated with Neptune or Poseidon, or the oceans.

Irregular satellites are named for the Nereids, daughters of Nereus and Doris and the attendants of Neptune. Triton is named after the son of Poseidon (the Greek god comparable to the Roman Neptune). Until the discovery of the second moon Nereid in 1949, Triton was commonly known as simply "the satellite of Neptune." CAPTION Triton (Moon) Facts Triton Triton Moon Facts Triton – photojournal.jpl.nasa.gov/catalog/PIA00317 Triton is Neptune’s largest moon and is the only large moon in the solar system to orbit in the opposite direction to its planet’s rotation, this is known as a retrograde orbit. Moon Profile 2.14 × 10^22 kg (29.1% Moon) Orbits: Triton size compared to the Moon and Earth Neptune moons size comparison (Proteus, Triton and Nereid) Facts about Triton Triton is a frozen wonderland, exhibiting a strange array of terrain types. Its icy surface has craters, geysers, and rugged landscape called “cantaloupe terrain”.

These all indicate some sort of activity going on inside, and cryovolcanism spouting material to the surface. The geysers of Triton spewing nitrogen gas out from beneath the surface into long plumes that rise as high as 8 kilometres. As a result, Triton has a very thin nitrogen atmosphere. The southern polar cap of Triton is covered with frozen nitrogen and methane. There may be a north polar cap as well. Triton could be divided into layers of ice around a rocky core. The crust is largely water ice. There could be subsurface ocean of slushy or liquid water. Triton orbits Neptune in retrograde — that is, opposite to the direction of Neptune’s rotation on its axis. This may imply that Triton was captured by Neptune’s gravity into its inclined orbit. Triton rotates once on its axis as it orbits the planet. It keeps the same face toward Neptune at all times. Triton will wander too close to Neptune in its orbit in about 3.5 billion years, and the gravitational pull of the planet will break Triton up. The result will be a ring system. Voyager 2 was the only spacecraft to visit and map Triton.

It flew by in 1989. There are no other missions planned to Neptune or Triton for the foreseeable future. Neptune's Moon Triton Triton From The Hubble Space Telescope This image of Triton was taken by the Hubble Space Telescope's Faint Object Camera in September of 1995. It was created from a blue and ultraviolet image. The color is false but closely matches the color observed from voyager images. Triton appears to be roughly 10% darker than in images taken by the Voyager 2 spacecraft. Also note that the equatorial region is bright, but there is a darker region around the pole. With Triton's long seasons, the southern summer has been progressing, and the south pole has received increasing sunlight; thus, it is probable that much of the frost covering the region in 1989 has evaporated, some of which may have condensed at the equator (hence the bright region there). This image truly pushes the limit of HST's resolving power. The image is centered at roughly 215 degrees latitude.

(Courtesy of Ted Stryk) South Pole of Triton This high resolution image of Triton was obtained by Voyager 2 on August 25, 1989. It shows the moon's south polar cap. One of the unusual aspect of this image is the dark streaks in the images. Perhaps they were made by geyser-like eruptions of nitrogen. The geyser eruptions could have carried darker materials from the crust. The light regions probably consist of layers of nitrogen. (Credit: Calvin J. Hamilton) Triton in 3D This is a computer-generated perspective rendering of one of the caldera -like depressions on Triton, as it would appear if viewed from the northeast. The image was obtained Aug. 24, 1989, when the Voyager spacecraft was about 181,800 kilometers (112,900 miles) from Triton. The caldera floor shown in this image is approximately 200 kilometers (120 miles) in diameter. It is extremely flat and probably was formed by the volcanic eruption of ice lavas of very low viscosity.

The bench visible in the foreground may be a remnant of earlier flooding to a level about 200 meters (600 feet) higher than the present caldera floor. (Courtesy NASA/JPL) Surface of Triton This is one of the most detailed views of the surface of Triton taken by Voyager 2 on its flyby of the large satellite of Neptune early in the morning of August 25, 1989. The picture was taken from a distance of 40,000 kilometers (25,000 miles), the frame is about 220 kilometers (140 miles) across and shows details as small as 750 meters (0.5 miles). Most of the area is covered by a peculiar landscape of roughly circular depressions separated by rugged ridges. This type of terrain, which covers large tracts of Triton's northern hemisphere, is unlike anything seen elsewhere in the solar system. The depressions are probably not impact craters: They are too similar in size and too regularly spaced. Their origin is still unknown, but may involve local melting and collapse of the icy surface.

A conspicuous set of grooves and ridges cuts across the landscape, indicating fracturing and deformation of Triton's surface. The rarity of impact craters suggests a young surface by solarsystem standards, probably less than a few billion years old. (Courtesy NASA/JPL) Dark Areas on Triton Voyager 2 acquired this black and white image of Triton during the night of August 24-25, 1989. Triton's limb cuts obliquely across the middle of the image. The field of view is about 1,000 km (600 miles) across. Three irregular dark areas, surrounded by brighter material, dominate the image. Low-lying material with intermediate albedo occupies the central area, and fresh craters occur along the right margin. Sub-parallel alignment of linear patches of dark material shown in the lower and left part of the image suggests that the patches are structurally controlled. (Courtesy NASA/JPL) Post Encounter Images of Triton This set of images shows the best views of Neptune's moon Triton taken by Voyager 2 as the spacecraft withdrew from the Neptune system on August 25, 1989.

The top four images were constructed from various color image bands as Voyager receded from Triton. (Courtesy Ted Stryk) Montage of Neptune and Triton This computer generated montage shows Neptune as it would appear from a spacecraft approaching Triton. The wind- and sublimation-eroded south polar cap of Triton is shown at the bottom of the Triton image, a cryovolcanic terrain at the upper right, and the enigmatic cantaloupe terrain at the upper left. Triton's surface is mostly covered by nitrogen frost mixed with traces of condensed methane, carbon dioxide, and carbon monoxide. The tenuous atmosphere of Triton, though only about one-hundredth of one percent of Earth's atmospheric density at the surface, is thick enough to produce wind-deposited streaks of dark and bright materials of unknown composition in the south polar cap region. The southern polar cap was sublimating at the time of the Voyager 2 flyby, as indicated by the irregular and eroded appearance of the edge of the cap.

The polar frosts were sublimating because Triton's orbital and rotational motion causes the sun to shine directly on the polar cap for a period of several decades during Neptune's and Triton's long austral summer. Though the polar cap was undergoing heat death, surface temperatures still were only about 38 K (-391 degrees Farenheit). (Courtesy NASA/JPL) Neptune on Triton's Horizon Composite view showing Neptune on Triton's horizon. Neptune's south pole is to the left; clearly visible in the planets' southern hemisphere is a Great Dark Spot, a large anticyclonic storm system located about 20 degrees South. The foreground is a computer generated view of Triton's maria as they would appear from a point approximately 45 km above the surface. The terraces visible in this image indicate multiple episodes of 'cryovolcanic' flooding. This three-dimensional view was created from a Voyager image by using a two-dimensional photoclinometric model. Relief has been exaggerated roughly 30-fold, the actual range of the relief is about 1 km. Would Neptune appear to be rising or setting?

Neither, due to the motion of Triton relative to Neptune, it would appear to move laterally along the horizon, eventually rising and setting at high latitudes. (Courtesy NASA/JPL) Triton Moon | PlanetsEdu.com Triton Triton Triton is one of Neptune’s moons. It was discovered in 1846 by the British astronomer William Lassell. Diameter: 2.71 x 106 m Mass: 2.14 x 1022 kg Composition: Nitrogen, water-ice, methane, carbon dioxide Orbit: 3.54 x 106 m from Neptune Triton is the largest of Neptune’s moons and the 7th largest moon in the Solar System. Neptune has 13 known moons. 6 are regular satellites with orbits in the same direction as the spin of the planet and there are 7 that orbit in the opposite direction to the planet’s spin. Neptune’s moons take their name from Roman and Greek water gods because of Neptune’s (Poseidon’s) position as the god of the sea. Triton was the son of Poseidon and the messenger of the ocean.

The name was first proposed by French astronomer Nicholas Camille Flammarion, though it was not adopted by the International Astronomical Union (IAU) until the 1950s. Triton is composed of a frozen nitrogen crust and an interior of water-ice, carbon-dioxide ice and some frozen methane and carbon monoxide. There may be surface ammonia and ammonia hydrates. The moon is coloured red as a result of tholins. These are organic compounds created by the ultraviolet irradiation of ethane and methane. There may be a small rocky core and a liquid water layer in the interior. Heat from the radioactive decay of the rock may cause convection currents within Triton’s mantle. Triton has a relatively flat surface, though there are features such as ridges, furrows, plateaus, plains and a few craters. Heights are usually less than one kilometre. The moon is geologically active. Some complex valleys and ridges could be the result of cryovolcanism – an extrusion of water-ice and ammonia rather than molten rock. There are a few eruptions of dust and nitrogen in plumes that reach heights of 8 km.

There are reflective frozen nitrogen and methane caps on the polar region that are marked with impact craters. The oldest terrain on Triton resembles the skin of a cantaloupe melon and is called “cantaloupe terrain”. This is mostly dirty water-ice with depressions of about 30 to 40 km in diameter. Triton’s atmosphere consists of nitrogen with additional traces of methane and carbon monoxide close to the surface. Turbulence on the surface of the moon creates weather conditions in its troposphere. There are no other higher atmospheric layers, such as the stratosphere on Earth that protects Earth from solar radiation. Consequently, a haze of hydrocarbons and nitriles – compounds of carbon and nitrogen such as cyanides – permeates through Triton’s troposphere. Triton has a retrograde orbit, meaning that it orbits in the opposite direction to Neptune’s spin. This implies that Triton was a captured object that originated in the Kuiper Belt, the region of outer space beyond Neptune. The orbit is synchronous, meaning that the moon itself spins on its own axis in the same direction as its orbital movement. Triton always keeps the same hemisphere facing Neptune.

It takes 5.87 Earth days to orbit Neptune. Along with Neptune and its other satellites, Triton takes 164.79 Earth years to orbit the sun. The only spacecraft flyby of Triton was Voyager 2 in 1989. Its closest approach to Triton was 37,790 km. Share this with the Universe! Triton Gallery BBC - Solar System - Triton (pictures, video, facts & news) Saturn, Neptune and Triton's future It is predicted that Saturn will lose its rings. In one hundred million years it is predicted that Saturn's rings will disappear. In one billion years, Neptune may develop its own rings when its moon Triton spirals from orbit and disintegrates into countless fragments. About Triton Triton is the largest natural satellite of the planet Neptune. It was discovered on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, an orbit in the opposite direction to its planet's rotation.

At 2,700 kilometres (1,700 mi) in diameter, it is the seventh-largest moon in the Solar System. Because of its retrograde orbit and composition similar to Pluto's, Triton is thought to have been a dwarf planet captured from the Kuiper belt. Triton has a surface of mostly frozen nitrogen, a mostly water-ice crust, an icy mantle and a substantial core of rock and metal. The core makes up two-thirds of its total mass. Triton has a mean density of 2.061 g/cm3 and is composed of approximately 15–35% water ice. Triton is one of the few moons in the Solar System known to be geologically active. As a consequence, its surface is relatively young with sparse impact craters, and a complex geological history revealed in intricate cryovolcanic and tectonic terrains. Part of its surface has geysers erupting sublimated nitrogen gas, contributing to a tenuous nitrogen atmosphere less than 1/70,000 the pressure of Earth's atmosphere at sea level.

Question: Triton is the largest moon of which planet?
Answer: Neptune